1. Field of the Invention
In general, the present invention relates to the production of zeolites.
2. Description of the Prior Art
Certain naturally occurring hydrated metal aluminum silicates are called zeolites. The synthetic adsorbents of the invention have compositions similar to some of the natural zeolites. The most common of these zeolites are sodium zeolites.
Certain adsorbents, including zeolites A, X and Y, selectively adsorb molecules on the basis of the size and shape of the adsorbate molecule and are called molecular sieves. Molecular sieves have a sorption area available on the inside of a large number of uniformly sized pores of molecular dimensions. With such an arrangement, molecules of a certain size and shape enter the pores and are adsorbed while larger or differently shaped molecules are excluded. Not all adsorbents behave in the manner of molecular sieves. The common adsorbents, charcoal and silica gel, for example, do not exhibit molecular sieve action.
Zeolites consist basically of a three-dimensional framework of SiO.sub.4 and AlO.sub.4 tetrahedra. The tetrahedra are cross-linked by the sharing of oxygen atoms so that the ratio of oxygen atoms to the total of the aluminum and silicon atoms is equal to two or O/(Al+Si)=2. The electrovalence of each tetrahedra containing aluminum is balanced by the inclusion in the crystal of a cation, for example a sodium ion. This balance may be expressed by the formula Al.sub.2 /Na.sub.2 =1. The spaces between the tetrahedra are occupied by water molecules prior to dehydration.
Zeolites may be activated by heating to effect the loss of the water of hydration. The dehydration results in crystals interlaced with channels of molecular dimensions that offer very high surface areas for the adsorption of foreign molecules. The interstitial channels of zeolite X are of a size such that heptacosafluorotributylamine and larger molecules will not enter into the channels. The interstitial channels of zeolite A will not accept molecules larger than 5.5 A.
Factors influencing occlusion by activated zeolite crystals are the size and polarizing power of the interstitial cation, the polarizability and polarity of the occluded molecules, the dimensions and shape of the sorbed molecule relative to those of the channels, the duration and severity of dehydration and desorption, and the presence of foreign molecules in the interstitial channels. It will be understood that the refusal characteristics of zeolites are quite as important as the adsorptive or positive adsorption characteristics. For instance, if benzene and heptacosafluorotributylamine (C.sub.4 F.sub.9).sub.3 N are to be separated, it is as essential that the crystals refuse the heptacosafluorotributylamine as it is that they absorb the benzene. If water and another material are to be separated, it is essential that the crystals refuse the other material as it is that they absorb the water.
Zeolites A, X and Y may be distinguished from other zeolite and silicates on the basis of their x-ray powder diffraction patterns and certain physical characteristics. The x-ray patterns for several of these zeolites are described below. The composition and density are among the characteristics which have been found to be important in identifying these zeolites.
The basic formula for all crystalline sodium zeolites may be represented as follows: EQU Na.sub.2 O:Al.sub.2 O.sub.3 :xSiO.sub.2 :yH.sub.2 O
In general, a particular crystalline zeolite will have values for x and y that fall in a definite range. The value x for a particular zeolite will vary somewhat since the aluminum atoms and the silicon atoms occupy essentially equivalent positions in the lattice. Minor variations in the relative numbers of these atoms does not significantly alter the crystal structure or physical properties of the zeolite. For zeolite X, an average value for x is about 2.5 with the x value falling within the range 2.5.+-.0.5. For zeolite A, the x value falls within the range 1.85.+-.0.5.
The value of y is not necessarily an invarient for all samples of zeolites. This is true because various exchangeable ions are of different size, and, since there is no major change in the crystal lattice dimensions upon ion exchange, the space available in the pores of the zeolite to accommodate water molecules varies.
The average value for y determined for zeolite X is 6.2. For zeolite A it is 5.1.
In zeolites synthesized according to the preferred procedure, the ratio Na.sub.2 O/Al.sub.2 O.sub.3 should equal one. But if all the excess sodium present in the mother liquor is not washed out of the precipitated product, analysis may show a ratio greater than one, and if the washing is carried too far, some sodium may be ion exchanged by hydrogen, and the ratio will drop below one. It has been found that due to the ease with which hydrogen exchange takes place, the ratio for zeolite X lies in the range of ##EQU1## The ratio for zeolite A lies in the range of ##EQU2## Thus the formula for zeolite A may be written as follows: EQU 1.0.+-.0.2Na.sub.2 O:Al.sub.2 O.sub.3 : 1.85.+-.0.5SiO.sub.2 :yH.sub.2 O
The formula for zeolite X may be written as follows: EQU 0.9.+-.0.2Na.sub.2 O:Al.sub.2 O.sub.3 :2.5.+-.0.5SiO.sub.2 :yH.sub.2 O
The formula for zeolite Y may be written as follows: EQU 0.9.+-.0.2Na.sub.2 O:Al.sub.2 O.sub.3 :4.5.+-.1.5SiO.sub.2 :yH.sub.2 O
"y" may be any value up to 6 for zeolite A; any value up to 8 for zeolite X; and any value up to 9 for zeolite Y.
The pores of zeolites normally contain water.
The above formulas represent the chemical analysis of zeolites A, X and Y. When other materials as well as water are in the pores, chemical analysis will show a lower value of y and the presence of other adsorbates. The presence in the crystal lattice of materials volatile at temperatures below about 600.degree. C. does not significantly alter the usefulness of the zeolite as an adsorbent since the pores are usually freed of such volatile materials during activation.
Among the ways of identifying zeolites and distinguishing them from other zeolites and other crystalline substances, the x-ray powder diffraction pattern has been found to be a useful tool. In obtaining the x-ray powder diffraction patterns, standard techniques were employed. The radiation was the K.alpha. doublet of copper, and a Geiger counter spectrometer with a strip chart pen recorder was used. The peak heights, I, and the positions as a function of 20 where 0 is the Bragg angle, were read from the spectrometer chart. From these, the relative intensities, EQU 100 I/I.sub.o
where I.sub.o is the intensity of the strongest line or peak, and d the interplanar spacing in A corresponding to the recorded lines were calculated.
X-ray powder diffraction data for sodium zeolite X are given in Table A. 100 I/I.sub.o and the d values in angstroms (A) for the observed lines for zeolite X are also given. The x-ray patterns indicate a cubic unit cell of dimensions between 24.5 A and 25.5 A. In a separate column are listed the sum of the squares of the Miller indices (h.sup.2 +k.sup.2 +l.sup.2) for a cubic unit cell that corresponds to the observed lines in the x-ray diffraction patterns. The a.sub.o value for zeolite X is 24.99 A, where a.sub.o is the unit cell edge.
TABLE A ______________________________________ X-RAY DIFFRACTION PATTERN FOR ZEOLITE X 100 I h.sup.2 + k.sup.2 + l.sup.2 I.sub.o d (A) ______________________________________ 3 100 14.47 8 18 8.85 11 12 7.54 19 18 5.73 27 5 4.81 32 9 4.42 35 1 4.23 40 4 3.946 43 21 3.808 44 3 3.765 48 1 3.609 51 1 3.500 56 18 3.338 59 1 3.253 67 4 3.051 72 9 2.944 75 19 2.885 80 8 2.794 83 2 2.743 88 8 2.663 91 3 2.620 96 1 2.550 104 -- -- 108 5 2.404 123 1 2.254 128 3 2.209 131 3 2.182 136 2 2.141 139 2 2.120 144 1 2.083 147 -- -- 155 -- -- 154 1 1.952 168 1 1.928 179 -- -- 184 1 1.842 187 -- -- 195 1 1.789 200 2 1.767 211 3 1.721 236 -- -- 243 3 1.603 ______________________________________
The more significant d values for zeolite X are given in Table B.
TABLE B ______________________________________ MOST SIGNIFICANT d VALUES FOR ZEOLITE X d Value of Reflection in A ______________________________________ 14.42 .+-. 0.2 8.82 .+-. 0.1 4.41 .+-. 0.05 3.80 .+-. 0.05 3.33 .+-. 0.05 2.88 .+-. 0.05 2.79 .+-. 0.05 2.66 .+-. 0.05 ______________________________________
X-ray powder diffraction data for sodium zeolite A are given in Table C.
TABLE C ______________________________________ X-RAY DIFFRACTION PATTERN FOR ZEOLITE A 100 I h.sup.2 + k.sup.2 +l.sup.2 d (A) I.sub.o ______________________________________ 1 12.19 100 2 8.71 69 3 7.11 35 4 -- -- 5 5.51 25 6 5.03 2 8 4.36 6 9 4.107 36 10 -- -- 11 3.714 53 12 -- -- 13 3.417 16 14 3.293 47 16 -- -- 17 2.987 55 18 2.904 9 20 2.754 12 21 2.688 4 22 2.626 22 24 2.515 5 25 2.464 4 26 -- -- 27 2.371 3 29 2.289 1 30 2.249 3 32 2.177 7 33 2.144 10 34 2.113 3 35 2.083 4 36 2.053 9 37 -- -- 38 -- -- 41 1.924 7 42 1.901 4 44 1.858 2 45 1.837 3 49 1.759 2 50 1.743 13 51 -- -- 53 1.692 6 54 1.676 2 57 1.632 4 59 1.604 6 61 1.577 4 62 -- -- 65 1.528 2 66 1.516 1 67 -- -- 68 -- -- 69 1.483 3 70 1.473 2 72 -- -- 74 1.432 3 75 1.422 2 77 1.404 5 81 1.369 2 82 1.360 8 a.sub.o 12.32 .+-. 0.02 ______________________________________
The more significant d values for zeolite A are given in Table D.
TABLE D ______________________________________ d VALUE OF REFLECTION IN A ______________________________________ 12.2 .+-. 0.2 8.6 .+-. 0.2 7.05 .+-. 0.15 4.07 .+-. 0.08 3.68 .+-. 0.07 3.38 .+-. 0.06 3.26 .+-. 0.05 2.96 .+-. 0.05 2.73 .+-. 0.05 2.60 .+-. 0.05 ______________________________________
Zeolite Y has a characteristic x-ray powder diffraction pattern which may be employed to identify zeolite Y. The x-ray powder diffraction data are shown in Table E. The values for the interplanar spacing d, are expressed in angstrom units. The relative intensities of the lines of the x-ray powder diffraction pattern are expressed as VS (very strong), S (strong), M (medium), W (weak), and VW (very weak).
TABLE E ______________________________________ X-RAY DIFFRACTION PATTERN FOR ZEOLITE Y Relative hkl h.sup.2 + k.sup.2 + l.sup.2 d,A Intensity ______________________________________ 111 3 14.37-14.15 VS 220 8 8.80-8.67 M 311 11 7.50-7.39 M 331 19 5.71-5.62 S 333,511 27 4.79-4.72 M 440 32 4.46-4.33 M 531 35 4.29-4.16 W 600,442 36 4.13-4.09 W 620 40 3.93-3.88 W 533 43 3.79-3.74 S 631 46 3.66-3.62 M 711,551 51 3.48-3.43 VW 642 56 3.33-3.28 S 733 67 3.04-3.00 M 822,660 72 2.93-2.89 M 751,555 75 2.87-2.83 S 840 80 2.78-2.74 M 911,753 83 2.73-2.69 W 664 88 2.65-2.61 M 844 96 2.54-2.50 VW 10,0,0;860 100 2.49-2.45 VW 10,2,0;862 104 2.44-2.40 VW 10,2,2;665 108 2.39-2.36 M 10,4,0;864 116 2.29-2.25 VW 11,1,1;775 123 2.24-2.21 VW 880 128 2.20-2.17 W 11,3,1;971,955 131 2.18-2.14 VW 11,3,3;973 139 2.10-2.08 W 12,0,0;884 144 2.07-2.04 VW 11,5,2;10,7,1;10,5,5 150 2.03-2.00 VW 10,8,2 168,171 1.92-1.89 VW 13,1,1;11,7,1;11,5,5;993 168,171 1,92-1.89 VW 13,3,1;11,7,3;977 179 1.86-1.83 VW 13,3,3;995 187,192 1.82-1.79 VW 888 187,192 1.82-1.79 VW 13,5,1;11,7,5 195 1.78-176 VW 14,2,0;10,10,0;10,8,5 200 1.76-1.73 W 13,5,4;11,8,5 210 1.71-1.69 W ______________________________________
Occasionally, additional lines not belonging to the pattern for the zeolite appear in a pattern along with the x-ray lines characteristic of that zeolite. This is an indication that one or more additional crystalline materials are mixed with the zeolite in the sample being tested. Frequently these additional materials can be identified as initial reactants in the synthesis of the zeolite, or as other crystalline substances. When the zeolite is heat treated at temperatures of between 100.degree. and 600.degree. C. in the presence of water vapor or other gases or vapors, the relative intensities of the lines in the X-ray pattern may be appreciably changed from those existing in the unactivated zeolite patterns. Small changes in line positions may also occur under these conditions. These changes in no way hinder the identification of these X-ray patterns as belonging to the zeolite.
The particular X-ray technique and/or apparatus employed, the humidity, the temperature, the orientation of the powder crystals and other variables, all of which are well known and understood to those skilled in the art of X-ray crystallography or diffraction can cause some variations in the intensities and positions of the lines. These changes, even in those few instances where they become large, pose no problem to the skilled X-ray crystallographer in establishing identities. Thus, the X-ray data given herein to identify the lattice for a zeolite, are not to exclude those materials, which, due to some variable mentioned or otherwise known to those skilled in the art, fail to show all of the lines, or show a few extra ones that are permissible in the cubic system of that zeolite, or show a slight shift in position of the lines, so as to give a slightly larger or smaller lattice parameter.
A simple test described in "American Minerologist," vol. 28, page 545, 1943, permits a quick check of the silicon to aluminum ratio of the zeolite. According to the description of the test, zeolite minerals with a three dimensional network that contains aluminum and silicon atoms in an atomic ratio of Al/Si=2/3=0.67, or greater, produce a gel when treated with hydrochloric acid. Zeolites having smaller aluminum to silicon ratios disintegrate in the presence of hydrochloric acid and precipitate silica.
The zeolites contemplated herein exhibit adsorbtive properties that are unique among known adsorbents. The common adsorbents, like charcoal and silica gel, show adsorption selectivities based primarily on the boiling point or critical temperature of the adsorbate. Activated zeolites on the other hand, exhibits a selectivity based on the size and shape of the adsorbate molecule. Among those adsorbate molecules, whose size and shape are such as to permit adsorption by zeolites, a very strong preference is exhibited toward those that are polar, polarizable, and unsaturated. Another property of zeolites that contributes to its unique position among adsorbents is that of adsorbing large quantities of adsorbate at either very low pressures, at very low partial pressures, or at very low concentrations. One or a combination of one or more of these adsorption characteristics or others can make zeolites useful for numerous gas or liquid separation processes where adsorbents are not now employed. The use of zeolites permits more efficient and more economical operation of numerous processes now employing other adsorbents.
Common adsorbents like silica gel and charcoal do not exhibit any appreciable molecular sieve action, whereas the various forms of zeolites do. The sieving action of zeolite X is shown by the following table in which P.sub.o represents the vapor pressure of the adsorbate at 25.degree. C. In this table as well as others in the specification the term "weight % adsorbed" refers to the percentage increase in the weight of the adsorbent. The adsorbents were activated by heating them at a reduced pressure to remove adsorbed materials. Throughout the specification the activation temperature for zeolite X was 350.degree. C., and the pressure at which it was heated was less than about 0.1 millimeter of mercury absolute unless otherwise specified. Likewise, the pressure given for each adsorption is the pressure of the adsorbate under the adsorption conditions unless the contrary is specified.
TABLE F ______________________________________ ADSORPTION DATA FOR ZEOLITE X Weight Temp. Pressure Percent Adsorbate (.degree.C.) (mm. Hg) Adsorbed ______________________________________ Octane 25 11 30.0 Benzene 25 45 25.0 m-Dichlorobenzene 25 P.sub.o 35.5 Heptacosafluorotributylamine 23 P.sub.o 2.2 ______________________________________
These data show that the porous structure of sodium zeolite X will permit free access to octane, benzene and dichlorobenzene molecules, so that they are readily adsorbed. But zeolite X is shown not to permit entry of the heptacosafluorotributylamine. This adsorptive behavior permits the separation of mixtures of heptacosafluorotributylamine and larger molecules from benzene, toluene, octane or other molecular species small enough to be adsorbed.
At about room temperature the sodium zeolite A adsorbs the C1 and C2 members of the straight chain saturated hydrocarbon series but not appreciable amounts of the higher homologs. Typical results are shown below.
TABLE G ______________________________________ ADSORPTION DATA FOR ZEOLITE A Weight Temp. Pressure Percent Adsorbate (.degree.C.) (mm. Hg) Adsorbed ______________________________________ Methane 25 700 1.6 Ethane 25 700 7.4 Propane 25 700 0.7 Butane 25 132 0.9 Octane 25 12 0.5 ______________________________________
This data suggests a process of using sodium zeolite A to remove methane and ethane from mixtures with propane and higher homologs of the series and with other larger molecules not appreciably adsorbed or with other gases less strongly adsorbed. The maximum dimension for ethane is 4.0 A, and for propane 4.9 A. The sodium zeolite A adsorbs the former but not appreciable amounts of the latter.
Zeolite Y has been found to have particularly good adsorption characteristics as is demonstrated by the representative adsorption data in Table H.
TABLE H ______________________________________ ADSORBATE DATA FOR ZEOLITE Y Weight Pressure Temp. Percent Adsorbate (mm. Hg) (.degree.C.) Adsorbed ______________________________________ H.sub.2 O 25 25 35.2 CO.sub.2 700 25 26.0 n-pentane 200 25 14.9 (C.sub.4 F.sub.9).sub.3 N 0.07 25 1.1 (C.sub.4 F.sub.9).sub.3 N 0.5 50 21.4 Krypton 20 -183 70.0 Oxygen 700 -183 35.7 ______________________________________
These data were obtained in the following manner:
Samples of zeolite Y which had been activated by dehydration at a temperature of approximately 350.degree. C., under vacuum, were tested to determine their adsorption properties. The adsorption properties were measured in a McBain-Baker adsorption system. The zeolite samples were placed in light aluminum buckets suspended from quartz springs. They were activated in situ, and the gas or vapor under test was then admitted to the system. The gain in weight of the adsorbent was measured by the spring extensions as read by a cathetometer. In Table H the pressure given for each adsorption is the pressure of the adsorbate. The term "weight percent adsorbed" in the table refers to the percentage increase in the weight of the activated adsorbent.
As may be seen from the adsorption data in Table H, activated zeolite Y can be employed to separate molecules having a critical dimension greater than that of heptocosafluorotributylamine from molecules having smaller critical dimensions. The critical dimension of a molecule is defined as the diameter of the smallest cylinder which will accommodate a model of the molecule constructed using the best available van der Waals radii, bond angles, and bond lengths.
A unique property of zeolite Y is its strong preference for polar, polarizable and unsaturated molecules, providing, of course, that these molecules are of a size and shape which permits them to enter the pore system. This is in contrast to charcoal and silica gel which show a primary preference based on the volatility of the adsorbate.
The reactivation or regeneration methods that may be used with zeolite Y differ from those used for the common adsorbents. Under the conditions of activation, reactivation or regeneration found to be satisfactory for zeolite Y, most other common adsorbents are either partially or completely destroyed by the heat or oxidized by the air. The conditions used for desorption of an adsorbate from zeolite Y vary with the adsorbate, but either one or a combination of raising the temperature and reducing the pressure, partial pressure or concentration of the adsorbate in contact with the adsorbent is usually employed. Another method is the displacement of the adsorbate by adsorption of another more strongly held adsorbate. For example, the desorption of occluded molecules from zeolite Y may be effected by washing with water or steam or by purging with a gas while heating, or by vacuum treatment.
Zeolite Y is distinguished from other molecular sieve types, for example, zeolite X described in U.S. Pat. No. 2,882,244, by its exceptional stability toward steam at elevated temperatures. This is a property which makes zeolite Y particularly suitable for such processes as gas drying, especially where the adsorbent bed must withstand numerous adsorption-desorption cycles. Zeolite Y is hydrolytically more stable than zeolite X. To demonstrate the improved hydrolytic stability afforded by zeolite Y, the data of Table I are presented. The relative hydrolytic stability was determined by measurement of the oxygen adsorption capacities of zeolite Y and zeolite X before and after heating in the presence of saturated steam at 410.degree. C. and atmospheric pressure for three hours.
TABLE I ______________________________________ COMPARISON OF ADSORPTION CAPACITIES OF ZEOLITE X AND ZEOLITE Y Percent of Zeolitic Molecular Molar SiO.sub.2 / Original Oxygen Capacity Sieve Al.sub.2 O.sub.3 Content Retained After Steaming* ______________________________________ X 2.2 11 X 2.5 9 X 2.7 17.5 Y 3.4 72 Y 3.8 80 Y 4.4 81 Y 4.6 87 Y 5.1 97 Y 5.3 90 ______________________________________ *Measured at -183.degree. C. and 100 mm.Hg.
Another means of differentiating zeolite Y compositions having a product silica-to-alumina molar ratio greater than 3 up to about 6 from zeolite X is by examination of the electrical properties of the particular species. The specific conductivity at several temperatures, as determined from resistance measurements made with specially constructed A.C. impedance bridges, and the values of activation energy (.DELTA.H) required for ionic conductivity in sodium zeolite X and sodium zeolite Y compositions are given in Table J below.
TABLE J ______________________________________ Specific Conductivity, Activation ohm.sup.-1 cm..sup.-1 Energy Zeolite Type and Molar at temperature (.DELTA.H), SiO.sub.2 /Al.sub.2 O.sub.3 Content 143.6.degree. C. 282.5.degree. C. Kcal./mole ______________________________________ X 2.4 2.0 .times. 10.sup.-5 8.0 .times. 10.sup.-4 12.0 X 3.0 5.4 .times. 10.sup.-6 2.1 .times. 10.sup.-4 12.2 Y 3.8 1.6 .times. 10.sup.-6 9.0 .times. 10.sup.-5 13.7 Y 4.5 2.4 .times. 10.sup.-7 2.4 .times. 10.sup.-5 15.6 Y 5.1 5.0 .times. 10.sup.-8 5.0 .times. 10.sup.-6 16.0 Y 5.3 -- 2.9 .times. 10.sup.-6* 16.3 ______________________________________ *Measured at 298.degree. C.
U.S. Pat. No. 2,882,243 describes a process for making zeolite A comprising preparing a sodium-aluminum-silicate water mixture having a SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio of from 0.5:1 to 2.5:1, a Na.sub.2 O/SiO.sub.2 mole ratio of from 0.8:1 to 3:1, and a H.sub.2 O/Na.sub.2 O mole ratio of from 35:1 to 200:1, maintaining the mixture at a temperature of from 20.degree. to 175.degree. C. until zeolite A is formed, and separating the zeolite A from the mother liquor.
U.S. Pat. No. 2,882,244 describes a process for making zeolite X comprising preparing a sodium-aluminum-silicate water mixture having a SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio of from 3:1 to 5:1, a Na.sub.2 O/SiO.sub.2 mole ratio of from 1.2:1 to 1.5:1, and a H.sub.2 O/Na.sub.2 O mole ratio of from 35:1 to 60:1, maintaining the mixture at a temperature of from 20.degree. to 120.degree. C. until zeolite X is formed, and separating the zeolite X from the mother liquor.
The process described in U.S. Pat. No. 3,101,251 is similar to that described in U.S. Pat. Nos. 2,882,243 and 2,882,244 except that the reaction mixture contains an admixture of non-kaolinitic aluminosilicate mineral and sodium hydroxide that has been fused at a temperature of between 330.degree. and 370.degree. C.
In U.S. Pat. No. 3,119,659, a kaolin clay and sodium hydroxide are formed into a compact body, dried, reacted in an aqueous mixture at a temperature of from 20.degree. to 175.degree. C. until a zeolite is formed. Zeolite A is formed in a reaction mixture having a Na.sub.2 O/SiO.sub.2 molar ratio of 0.5:1 to 1.5:1, a SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of 1.6:1 to 2.4:1 and a H.sub.2 O/Na.sub.2 O molar ratio of 20:1 to 100:1. Zeolite X is formed in a reaction mixture having a Na.sub.2 O/SiO.sub.2 molar ratio of 1.5:1, a SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of 5:1, and a H.sub.2 O/Na.sub.2 O molar ratio of 30:1 to 60:1. Zeolite Y is formed in a reaction mixture having a Na.sub.2 O/SiO.sub.2 molar ratio of 0.5:1, a SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of 7:1, and a H.sub.2 O/Na.sub.2 O molar ratio of 20:1 to 40:1.
In U.S. Pat. No. 3,130,007 zeolite Y is formed by preparing an aqueous sodium alumino silicate mixture having a certain composition, maintaining the mixture at a temperature of 20.degree. to 125.degree. C. until zeolite Y is formed, and separating the zeolite Y from the mother liquor. Table K shows reaction mixture compositions that produce zeolite Y.
TABLE K ______________________________________ U.S. Pat. No. 3,130,007 REACTION MIXTURE COMPOSITIONS FOR ZEOLITE Y Na.sub.2 O/SiO.sub.2 SiO.sub.2 /Al.sub.2 O.sub.3 H.sub.2 O/Na.sub.2 O ______________________________________ 0.20-0.40 10-40 25-60 0.41-0.60 10-30 20-60 0.61-0.80 7-30 20-60 0.6-1.0 8-30 12-90 1.5-1.7 10-30 20-90 1.9-2.1 10 40-90 ______________________________________
U.S. Pat. No. 3,130,007 indicates on column 2, lines 35-42 the necessity of using an active silica source by specifying that aqueous colloidal silica sols or reactive amorphous solid silicas are preferred.
In U.S. Pat. No. 4,016,246 zeolite Y is formed by preparing an aqueous alumino silicate reaction mixture by mixing an alumina component and a Na.sub.2 O component with an active hydrated sodium metasilicate to form a certain reaction mixture, then heating the mixture at a temperature of 20.degree. to 120.degree. C. until zeolite Y is formed. Table L shows reaction mixture compositions that produce zeolite Y.
TABLE L ______________________________________ U.S. Pat. No. 4,016,246 REACTION MIXTURE COMPOSITIONS FOR ZEOLITE Y Na.sub.2 O/SiO.sub.2 SiO.sub.2 /Al.sub.2 O.sub.3 H.sub.2 O/Na.sub.2 O ______________________________________ 0.28-&lt;0.30 8-10 20-70 0.30-&lt;0.31 8-12 20-70 0.31-&lt;0.32 8-14 20-70 0.32-&lt;0.34 8-16 12-90 0.34-&lt;0.40 7-40 12-120 0.4-&lt;0.7 5-50 12-120 0.7-1.0 31-50 12- 120 ______________________________________
U.S. Pat. No. 4,016,246 also discusses the significance of using an active source of sodium silicate. In that patent, active hydrated sodium metasilicate is prepared by carefully hydrating sodium metasilicate under specified conditions.
From the prior art one would assume that zeolite A cannot be made from reaction mixtures having a SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio greater than 2.5:1 that zeolite X cannot be made from reaction mixtures having a SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio greater than 5:1; and that zeolite Y cannot be made from an unreactive source of silica. Nothing in the prior art teaches that a combination of zeolite A and zeolite X can be formed in the same reaction.